1. Field of the Invention
This invention relates to a transition radiation interference spectrometer and in particular to a transition radiation interference spectrometer for measuring the energy and divergence of a charged particle beam.
2. Description of the Prior Art
In attempting to define the behavior of a charged particle beam, scientists for some time have focused on determining the emittance of the beam. Briefly stated, the emittance is a way of describing the beam quality in terms of its divergence at various points within its cross-section. A detailed discussion of emittance and its use in beam diagnostics can be found in "Emittance and Brightness: Definitions and Measurements", by Lejeune and Aubert in Advances in Electronics and Electron Physics, Supplement 13A, 1980.
It is also known in the prior art that beam emittance can be determined once the charged particle beam's energy, divergence and current density profile have been determined. Older methods of determining these quantities have made use of collimators and screens which are cumbersome, expensive and usually restricted to placement at only one fixed beamline location. The collimators and screens also suffer from electron permeability for high energy beams thereby restricting their usefulness. The phosphor screens used have a slow response time and poor spacial resolution. They are also limited in use to large diameter beams on the order of a few centimeters.
Another prior art method makes use of wire scanners placed at multiple stations along the charged particle beam. However, real-time measurements are not possible since the wires need to be scanned successively to determine the beam profiles at each of the multiple stations. It is also known in the prior art to combine the use of focusing magnets with wire scanners. However, this method suffers from the requirement of multiple station beam profile scans as a function of magnet strength and, as such, is not capable of real-time measurement. Still another method makes use of multiple, non-interactive wall current monitors placed along a beam path. However, use of these monitors requires elaborate mathematical analysis to produce an emittance value since multipole moments of the measured beam profiles must be calculated. In addition, all multi-position devices and measurements are sensitive to beam centroid motion and require detailed knowledge of beam particle trajectories and beam profiles. These devices cannot be used to make time resolved measurements or serve as real-time monitors for either beam profile or beam divergence measurements since they typically require lengthy periods of time (several minutes to hours) for data acquisition. Beam energy is typically determined by using magnetic fields to bend the beam through a trajectory that is a function of beam energy.